1. Field of the Invention
The present invention relates to a binder resin that is used for an electrophotographic toner that can be used in an electrophotographic device such as a copy machine, a printer or a facsimile machine that makes use of an electrophotographic process, an electrophotographic toner using the same and a manufacturing method thereof, an electrophotographic developer, and an image forming method.
2. Description of the Related Art
Many electrophotographic methods are known (for example, see Japanese Patent Application Publication (JP-B) No. 42-23910). In general, through a plurality of processes by various means, an electrical latent image is formed on a surface of a photoreceptor (latent image holding body) that makes use of a photoconductive material, then after the formed latent image is developed by use of a toner to form a toner image, the toner image on the surface of the photoreceptor, is transferred onto a surface of a transfer receiving material such as paper with or without the use of an intermediate transfer body, and the transferred image is fixed by heating, pressing, heating and pressing or a solvent vapor, whereby a fixed image is formed. If necessary, the toner that remains on a surface of the photoreceptor is clean by various methods and supplied again to the above plurality of processes.
As a fixing technique for fixing an image transferred onto a surface of the transfer receiving material, a heating roller fixing method in which and a pressure roller, a transfer receiving material onto which a toner image is transferred is inserted between a pair of rollers including a heating roller for fixing is generally used. Furthermore, as a similar technique, one constituted by replacing one or both of rollers with a belt or belts is also known. These techniques, in comparison with other fixing methods, can generate strong fixed images at high speed, are higher in energy efficiency, and cause less damage to the environment by volatilization of solvents and so on.
On the other hand, in order to reduce the amount of energy used by a copy machine or a printer, a technique that can fix a toner with lower energy is desired. Accordingly, an electrophotographic toner that can be fixed at lower temperatures is strongly demanded.
As a means for lowering a fixing temperature of a toner, a means for lowering a glass transition temperature of a toner resin (binder resin) is used. As a toner binder resin, polyester can be used, and, in particular for electrophotography, a crystalline polyester resin is used. The polyester contains acid groups and hydroxyl groups and is liable to be affected by its environment, and in particular, humidity. As attempts to improve chargeability, a proposal to make an acid value of resin lower (Japanese Patent Application Laid-Open (JP-A) No. 62-291668), and proposals to use an organic fluorinated compound (JP-A No. 11-24306 or 2003-107802) are disclosed; however, these are insufficient in the chargeability.
Furthermore, as a toner that uses a rare earth element compound, one in which an α-Si photoreceptor, a monocomponent magnetic toner, and a combination of a rare earth fluoride element compound and a rare earth oxide element compound is disclosed (for example, JP-A Nos. 20022000-311769 and 2002-311639). Still furthermore, a toner that uses a binder resin and a toner that uses cerium oxide and a rare earth element compound as external additives are disclosed (for example, JP-A No. 2002-341587 and 2001-265057).
All examples use a method in which a rare earth compound is externally added on a surface of a toner and are intended to improve cleaning defects.
On the other hand, recently, in view of reduction in environmental burden (reduction of CO2 gas), energy-saving manufacturing methods have been proposed. In the field of electrophotography (for example, JP-A No. 10-26842), from the viewpoint of energy saving, there is strong demand in the market for reduction in the amount of energy used to manufacture toner and the amount of energy that a printer or a copy machine uses.
As to a manufacturing method of toners, from conventional processes such as melt kneading, pulverizing and classifying, a suspension polymerizing method and a melt-suspension method have been developed, and from the viewpoint of the manufacturing energy, reduction thereof is progressing.
However, the energy necessary for the manufacture of toner resin has not yet been sufficiently reduced.
In particular, in the case of polyester resins that can lower fixing energy, in comparison with vinyl polymerization resins, much energy is still consumed in the manufacture thereof. Accordingly, the total energy consumed in the manufacture of the resin and the toner is great.
For example, in the manufacture of toner resins, so far, tin-based catalysts including dibutyl tin oxide and titanium-based catalysts including titanium oxide have generally been used. As catalysts for polymerizing polyester, dialkyl tin oxide, dialkyl tin carboxylate, hydroxymonoalkyl tin oxide, and dialkyldistannoxane have been used as a catalysts for polyester resin. For example, in JP-A Nos. 51-61595 and 62-87248, a polymerization method that uses dialkyldistannoxane is proposed, and in JP-A Nos. 03-188047 and 04-288041, a polymerization method that uses organic tin is proposed. However, when, a high molecular weight polymer compound necessary for imparting viscoelasticity and durability to toner is manufactured using these methods, there are problems in that reaction conditions of a high temperature (150° C. or more) and a low vacuum are necessary, and in that it is difficult to recover and reuse the catalyst after the reaction. Accordingly, it is difficult to regard these methods as industrially sufficient methods.
As a method for overcoming the problem of recovering a catalyst, for example in JP-A No. 2003-335727, a method in which two kinds of solvent are used to conduct polymerization and a catalyst is extracted in one solvent layer is proposed. However, a special fluorinated solvent is necessary in the method. Furthermore, since a Lewis acid is used as the catalyst that is used in the polycondensation, the catalyst is decomposed by water and difficult to recover and reuse.
On the other hand, the present inventors synthesized a polyester resin by use of a rare earth triflate catalyst and tried to prepare a toner using the polyester resin. However, the toner was found to have a defect in that a long-term storability of an image was poor. Furthermore, it was also found that since a low molecular weight component was present in the polyester resin, the fixing strength became poor.